The present invention concerns a portable incandescent light assembly with a selectably interposable filter. For example, it may be capable of interposing a colored filter in the path of a white-light source, or of providing white light either with or without infra-red light.
The present invention is particularly applicable to situations involving night vision for airplane pilots. For such night vision, it has been common to provide infra-red search-lights on an airplane, for viewing outside scenes. The pilot may be provided with sensitive infra-red nightvision goggles, which can view the intra-red-illuminated scenes. However, infra-red sources within the airplane (such as instrument panel lights) may interfere with viewing through the plane windscreen by causing reflections of undesired infra-red light into the night vision goggles. During such night-vision situations, it is also desirable to be able to read maps or the like, as during flight. For example, a co-pilot may desire to view a map under visible light while the pilot is wearing night-vision goggles. Under these circumstances a source of infra-red light in the cockpit would interfere with the pilot's functioning.
The present light assembly provides a blue or green filter, which in one position filters out infra-red light (e.g. an Anvis Green A light) from an incandescent lamp while allowing visible light to pass. In this situation, the light emission from the light assembly does not add to infra-red radiation within the cockpit and so does not interfere with the pilot's night-vision functioning. In a second position, the present invention permits emission of unfiltered white light (including infra-red light) from the lamp for ordinary use where night-vision is not a factor.
The present invention is particularly concerned with the control of a filter, to flip it between a position across the axis of the light assembly (where the filter is interposed in the path of the light output to filter out undesired light) to a position parallel to the axis, at which the filter is relatively ineffective and all light (e.g. both infra-red and visible light from the lamp) is output for illumination purposes. According to a further specific feature of the invention, a light seal is provided which avoids undesired (e.g. infra-red) light spill-out when the filter is in the transverse position.
In addition, the light assembly may be selectably used as a flood-lamp or a spot-light, by moving the lamp bulb assembly in an axial direction.